This core will provide a centralized service for producing transgenic mice. Specifically, the core will undertake the following procedures: (1) microinjection of fertilized one-cell mouse eggs with specific DNA constructs prepared by Program Project investigators, (2) return the eggs to pseudopregnant foster mothers, (3) screen for transgenic offspring by Southern analysis of DNA isolated from tails, and (4) assist in the dissection and analysis of tissues from transgenic mice and embryos. Therefore, in addition to providing an increasingly important research tool for members of the DRTC who may wish to establish the technique, or collaborate on projects related to the expression and mode of action of factors regulating growth and differentiation in vivo.